Buffering

import { Grid } from 'cx/widgets';

Grid supports buffered rendering which dramatically improves performance with large datasets. Instead of rendering all rows, only visible rows plus a buffer are rendered, enabling smooth scrolling with thousands of records.

 <div controller={PageController}>
  <Grid
    records={m.records}
    keyField="id"
    buffered
    style="height: 400px"
    mod={["fixed-layout", "contain"]}
    cached
    selection={{ type: KeySelection, bind: m.selection }}
    columns={[
      {
        header: "#",
        align: "center",
        children: <div class="cxe-grid-row-number" />,
        defaultWidth: 70,
      },
      {
        header: { text: "Name", style: "width: 100%" },
        field: "fullName",
        sortable: true,
        resizable: true,
      },
      {
        header: "Continent",
        field: "continent",
        sortable: true,
        resizable: true,
        defaultWidth: 130,
      },
      {
        header: "Browser",
        field: "browser",
        sortable: true,
        resizable: true,
        defaultWidth: 100,
      },
      {
        header: "Visits",
        field: "visits",
        sortable: true,
        align: "right",
        resizable: true,
        defaultWidth: 70,
      },
    ]}
  />
</div> 
 class PageController extends Controller {
  onInit() {
    this.store.init(
      m.records,
      Array.from({ length: 5000 }, (_, i) => ({
        id: i + 1,
        fullName: names[i % 5],
        continent: continents[i % 5],
        browser: browsers[i % 5],
        visits: Math.floor(Math.random() * 100) + 1,
      })),
    );
  }
} 
 interface Record {
  id: number;
  fullName: string;
  continent: string;
  browser: string;
  visits: number;
}

interface PageModel {
  records: Record[];
  selection: number;
}

const m = createModel<PageModel>(); 
 import { createModel } from "cx/data";
import { Controller, KeySelection } from "cx/ui";
import { Grid } from "cx/widgets"; 

Name	Continent	Browser	Visits
Alice Johnson	North America	Chrome	30
Bob Smith	Europe	Firefox	40
Carol White	Asia	Safari	10
David Brown	South America	Edge	18
Eva Green	Africa	Opera	23
Alice Johnson	North America	Chrome	52
Bob Smith	Europe	Firefox	41
Carol White	Asia	Safari	12
David Brown	South America	Edge	34
Eva Green	Africa	Opera	3
Alice Johnson	North America	Chrome	77
Bob Smith	Europe	Firefox	17
Carol White	Asia	Safari	68
David Brown	South America	Edge	46
Eva Green	Africa	Opera	45
Alice Johnson	North America	Chrome	97
Bob Smith	Europe	Firefox	81
Carol White	Asia	Safari	49
David Brown	South America	Edge	42
Eva Green	Africa	Opera	40
Alice Johnson	North America	Chrome	31
Bob Smith	Europe	Firefox	87
Carol White	Asia	Safari	52
David Brown	South America	Edge	75
Eva Green	Africa	Opera	84
Alice Johnson	North America	Chrome	72
Bob Smith	Europe	Firefox	57
Carol White	Asia	Safari	27
David Brown	South America	Edge	100
Eva Green	Africa	Opera	63
Alice Johnson	North America	Chrome	46
Bob Smith	Europe	Firefox	22
Carol White	Asia	Safari	66
David Brown	South America	Edge	70
Eva Green	Africa	Opera	93
Alice Johnson	North America	Chrome	64
Bob Smith	Europe	Firefox	46
Carol White	Asia	Safari	93
David Brown	South America	Edge	77
Eva Green	Africa	Opera	72
Alice Johnson	North America	Chrome	7
Bob Smith	Europe	Firefox	79
Carol White	Asia	Safari	60
David Brown	South America	Edge	27
Eva Green	Africa	Opera	95
Alice Johnson	North America	Chrome	10
Bob Smith	Europe	Firefox	14
Carol White	Asia	Safari	6
David Brown	South America	Edge	31
Eva Green	Africa	Opera	92
Alice Johnson	North America	Chrome	98
Bob Smith	Europe	Firefox	43
Carol White	Asia	Safari	35
David Brown	South America	Edge	67
Eva Green	Africa	Opera	17
Alice Johnson	North America	Chrome	45
Bob Smith	Europe	Firefox	85
Carol White	Asia	Safari	12
David Brown	South America	Edge	60
Eva Green	Africa	Opera	78

This grid contains 5,000 rows but renders smoothly thanks to buffered mode. Try scrolling and sorting to see the performance.

How It Works

Enable buffered mode by setting the buffered property. The grid calculates which rows are visible and renders only those plus a configurable buffer for smooth scrolling.

<Grid
  records={m.records}
  buffered
  style="height: 400px"
  mod={["fixed-layout", "contain"]}
  cached
  columns={columns}
/>

For optimal performance, combine buffering with:

Fixed height - The grid needs a fixed height to calculate visible rows
mod="fixed-layout" - Uses CSS table-layout: fixed for faster rendering
mod="contain" - Adds CSS containment for better browser optimization
cached - Prevents row re-renders when unrelated store data changes

Row Numbers

Use the built-in cxe-grid-row-number class to display automatic row numbers:

{
  header: "#",
  defaultWidth: 50,
  children: <div class="cxe-grid-row-number" />
}

Configuration

Property	Type	Description
`buffered`	`boolean`	Enables buffered rendering mode.
`bufferSize`	`number`	Number of rows to render outside the visible area. Default is `60`.
`bufferStep`	`number`	Number of rows to add/remove when scrolling. Default is `15`.
`cached`	`boolean`	Prevents row re-renders when unrelated store data changes. Rows only update when their record data changes.
`lockColumnWidths`	`boolean`	Locks column widths to prevent layout shifts during scrolling.
`lockColumnWidthsRequiredRowCount`	`number`	Minimum number of rows required before column widths are locked.
`measureRowsOnScroll`	`boolean`	Re-measures row heights while scrolling. Useful for variable height rows.